(1) Field of the Invention
The present invention generally relates to a thin-film magnetic head, and more particularly to a thin-film magnetic head mounted on a swing-type actuator (a rotary actuator) in a magnetic disk device.
Magnetic disk devices are being miniaturized, so that the diameter of the magnetic disk used in each of them is decreased by about 1.8 inches. Due to the decrease of the diameter of the magnetic disk, the velocity of the magnetic head relative to the magnetic disk is decreased. In addition, to prevent the recording capacity of the miniaturized magnetic disk from being decreased, recording tracks must be formed at a high density on the magnetic disk. Thus, it is required that the thin-film magnetic head function normally even if the relative velocity of the magnetic head to the magnetic disk is decreased and even if the recording tracks are formed at a high density on the magnetic disk.
(2) Description of the Related Art
FIGS. 1A and 1B indicate a structure of a conventional thin-film magnetic head disclosed, for example, in Japanese Laid-Open Patent Application No. 61-276110. FIG. 1A is a cross sectional view of the conventional thin-film magnetic head and FIG. 1B is a view thereof projected on the surface of the magnetic disk.
Referring to FIGS. 1A and 1B, the thin-film magnetic head 10 has a substrate 11, a reproducing head part 15 and a recording head part 13. The reproducing head part 15 is stacked on the substrate 11, and further, the recording head part 13 is formed on the reproducing head part 15. The reproducing head part 15 has an insulating layer 19, a first magnetic layer 16, an insulating layer 19a, a second magnetic layer 17 and a magnetoresistance effect element (hereinafter referred to as an MR element) 14. The insulating layer 19 is formed on the substrate 11, and a structure in which the insulating layer 19a is positioned between the first magnetic layer 16 and the second magnetic layer 17 is stacked on the insulating layer 19. The MR element 14 is provided in the insulating layer 19 so as to face the surface 100 of the magnetic disk. In this reproducing head part 15, a reproducing gap 22 is formed between ends of the first and second magnetic layers 16 and 17 so as to face the surface 100 of the magnetic disk. The recording head part 13 has a structure in which an insulating layer 20a is sandwiched between the second magnetic layer 17 and a third magnetic layer 18, an insulating layer 20 covering the third magnetic layer 18 and coils 12 provided in the insulating layer 20a. A recording gap 21 is formed between ends of the second and third magnetic layers 17 and 18. The magnetic layers 16, 17 and 18 are made of NiFe (permalloy).
In the reproducing head part 15, the first magnetic layer 16 and the second magnetic layer 17 function as shield layers, and in the recording head part 13, the second magnetic layer 17 and the third magnetic layer 18 function as magnetic poles. That is, the second magnetic layer 17 is shared by both the reproducing head part 15 and the recording head part 13. This type of magnetic head is often referred to as a sharing type magnetic head. Another type of magnetic head is referred to, for example, as a separate type magnetic head. In the separate type magnetic head, the reproducing head part 15 and the recording head part 13 have two shield layers and two magnetic poles respectively. Thus, an interval (a) between the recording gap 21 and the reproducing gap 22 in the sharing type magnetic head can be narrower than that in the separate type magnetic head. The interval (a) between the recording gap 21 and the reproducing gap 22 is referred to as a gap interval (a).
According to the thin-film magnetic head having the above structure, information is reproduced from the magnetic disk via the MR element 14 of the reproducing head part 15. Thus, even if the relative velocity of the thin-film magnetic head 10 to the magnetic disk is small, reproducing signals having high levels can be obtained.
The above gap interval (a) depends on the thickness (t) of the second magnetic layer 17. Here, if it is assumed that the magnetic coercive force H.sub.c of the recording layer of the magnetic disk is equal, for example, to 1,800 Oe (oersted), a recording magnetic field strength equal to or greater than 3,600 Oe which is twice the magnetic coercive force H.sub.c is required to securely record signals in the recording layer of the magnetic disk. Since the saturation magnetic flux density B.sub.s of NiFe forming the magnetic layer 17 is equal to 1 T (tesla), the thickness (t) of the magnetic layer 17 must be equal to or greater than 2.4 .mu.m to form a magnetic field having a magnetic field strength equal to or greater than 3,600 Oe in the space facing the end of the magnetic layer 17 (see a line I in FIG. 4). Thus, the conventional thin-film magnetic head has the gap interval (a), for example, of about 5 .mu.m.
The thin-film magnetic head having the above structure is mounted at the end of a swing-type actuator which pivots on the other end thereof. Due to the pivoting of the swing-type actuator having the thin-film magnetic head, the angle between the direction of the thin-film magnetic head and the direction in which tracks of the magnetic disk runs varies. This angle is referred to as the yaw angle. A width of an area on which information is not reproduced to the variation of the yaw angle is defined as a yaw angle loss. Detailed description of the yaw angle and the yaw angle loss will be given later.
For example, in a case where the yaw angle of the swing-type actuator on which the above thin-film magnetic head is mounted is 10 degrees, the yaw angle loss has a large value of 1.75 .mu.m. The larger the yaw angle loss, the smaller the width of a part of each track of the magnetic disk which part effectively faces the MR element 14 in the reproducing gap 22 of the thin-film magnetic head 10. Thus, if the yaw angle loss is large, it is difficult to reproduce a signal having a high quality. In addition the large yaw angle loss prevents the recording tracks from being formed at a high density on the magnetic disk.